Pistorius said: "I would like to take this opportunity to apologise to Mrs and Mr Steenkamp, to Reeva's family, to those of you who knew her who are here today.

"There is not a moment, and there hasn't been a moment since this tragedy happened, that I haven't thought about your family."

Pistorius continued: "I wake up in the morning and you are the first people I think of, the first people I pray for. I can't imagine the pain and the emptiness and the sorrow that I have cause you.

"I was simply trying to protect Reeva, I can promise that when she went to bed that night she felt love. I have tried to put my words on paper many, many times to write to you, but no words would suffice."

Answering questions from his lawyer Barry Roux, Pistorius told the jury that he has taking anti-depressants and medication to help him sleep.

"I am so scared to sleep for several reasons", he said. "I have terrible nightmares about things that happened that night, where I can smell the blood, and I wake up to being terrified, just in a complete state of terror, to a point where I would rather not sleep than sleep and wake up to that."

Pistorius also said that he doesn't "ever want to handle a firearm again or be around a firearm."

Earlier, Pistorius sobbed and sat with his hands over his head while graphic descriptions of Steenkamp's injuries were read out.

Prosecutors claim that Pistorius killed Ms Steenkamp in February 2013 after an argument. He has denied prosecution allegations that he shot her deliberately, testifying that he mistook her for an intruder.